You can replace the sender w/o removing the gas tank - I know , I did
it (on my '77). What you do is cu a hole in the sheet metal right over
the sender. Then you pull the old sender, put in a new one, and patch up
up the hole!  It is kind of nerve wracking cutting a hole directly above
the fuel tank- but I had exact instructions from a trust worthy freind
as to where to cut.

If you want details, let me know.
      Bill Hollings